The invention concerns an optical circulation device for coupling in a laser beam, and a method of positioning a laser beam.
In industry, pulsed lasers are used more and more. In order to achieve higher productivities, it is tried to increase the volume of material per unit of time that is to be treated by laser beams. This is accomplished by a scaling of power of laser systems. Laser machining processes are usually carried out in a certain pulse energy range. For this reason, increasing average power in general requires increasing pulse repetition rate in order to maintain the pulse energy within the desired range.
Pulsed laser radiation for material machining may be generated for example in the following ways: Q-switched resonators, oscillators, and (regenerative) amplifiers. For short-pulse lasers having a pulse duration of less than a nanosecond, which are required for cold ablation, Q-switched resonators are not suitable for the reason that pulse formation is too slow. Oscillators so far do not achieve sufficiently high pulse energies for broad fields of application, for which reason pulses are boosted using linear or regenerative amplifiers, decreasing the repetition rate. Due to technological progress, the average powers that can be achieved with oscillators are rising continuously. Oscillators suited for industrial application for reasons of stability can have only short resonator lengths and therefore emit their power in pulses of high repetition rate, typically several megahertz, and comparatively low pulse energy.
In material processing, there now arises the problem that the pulses have to be separated individually, which has to be done sufficiently fast in between the individual laser pulses, in order to impinge upon a workpiece in different positions. Typically, in material processing using lasers, different positions of the workpiece are to be treated successively with the laser. One exemplary application is for example edge isolation of solar cells, where a line of individual laser pulses overlapping in a defined way is drawn along the workpiece. Also in numerous other applications, for example marking or surface treatment, the pulsed laser beam is moved relative to the surface of the workpiece. In order to generate this relative movement of the laser pulse beam relative to the workpiece, one can either change the position of the workpiece, which is a slower alternative, or scan the laser across the fixed or slowly moving workpiece, as a faster alternative.
Known laser scanner systems use moving optics, such as mirrors, where the maximum positive and negative acceleration thereof for positioning a laser beam imposes limits in speed for the system. Rotating prisms, glass bodies, and so on operate with a constant velocity respectively angular velocity, however, their positioning speed is limited in mechanical regards and due to stability reasons so that they cannot be used for the high repetition rates described above.
A further application of pulsed lasers in micro material machining is for example drilling tiny holes. For helical drilling, an optics having optical components rotating at very high speeds is used to position individual laser pulses. The beam positioning speed is limited by mechanical factors and for reasons of stability.
The invention is based on the object of providing a device respectively a method that allows for a very fast beam positioning of laser beams, in particular pulsed laser beams.